1. Field of the Invention
This invention relates generally to the field of vibration dampers adapted for damping torsional vibrations in rotating shafts such as the crankshaft of an internal combustion engine, and pertains particularly to a uniform strain damper.
2. Description of the Prior Art
Torsional vibration dampers have been well known in the art. Multi-throw crankshafts of internal combustion engines, for examples, are caused to vibrate torsionally at certain engine speeds because of the forces to which they are subjected during engine operation. Unless such vibrations are damped, the engine may operate roughtly over the range of speeds at which the amplitude of torsional vibration at the crankshaft is high, and the vibration may become so excessive as to cause breakage of the crankshaft or connected parts. In order to prevent the harmful effects of such torsional vibration, it is common practice to secure a vibration damper to one end of the crankshaft. The vibration damper usually takes the form of a mass adapted to rotate with the crankshaft, and secured to the crankshaft by means of a suitable resilient material, such as rubber. When a vibration damper is applied to a crankshaft, it is usually secured to the end of the crankshaft opposite the flywheel. Because of its inertia, natural frequency of vibration and damping in the suspension material itself, it provides an added mass to that end of the crankshaft subject to the greatest torsional vibration and has the effect of maintaining the amplitude of such vibrations within predetermined limits.
The mounting of the damper to the crankshaft or like member may take various forms, and does not form a part of the present invention. Various methods of mouting the damper are well known to persons of ordinary skill in the art, and are exemplified in the prior art patents discussed hereafter. To this extent, the following patents are hereby incorporated by reference into the present description. By way of example, the inertia member in the form of a ring has typically been resiliently connected to the shaft or other rotatable member, such as a pulley, adapted to be connected to the shaft.
A typical form of such dampers has comprised a rotor disk having a hub portion arranged to be secured to the end of a crankshaft or the like, and radially extending annular body flange portion on which is corrotatively mounted an inertia mass yieldably coupled to the hub body flange in a manner to effect attenuation of torsional crankshaft vibrations due to the inertial resistance of the inertia mass. In some of these dampers the coupling has been primarily or entirely elastomeric, i.e., rubber whether natural or artificial or a combination thereof. Other of these prior art dampers have comprises a combination of rubber and viscous coupling means, wherein rubber tuning ring means maintain a shear film spacing between parallel surfaces of the inertia mass and body flange in which biscous damping medium such as a silicone fluid is filled.
The connecting rubber component of vibration dampers of the described type are typically annular in configuration, with the component being relatively thin and extending in a radial direction. The inner hub extends within the rubber component, and the inertia ring typically surrounds the outer surface of the rubber component. In certain prior art devices, the rubber component has been a flat, constant thickness member, but these have the disadvantage of having the outer parts of the member being highly strained. This results in slightly higher damping, but much lower stiffness, fatigue life and abrasion resistance.
Some advantage has been achieved by having the rubber component increase in axial thickness with increasing radial extension. Torsional dampers having such rubber components of varying thickness are shown, for example, in U.S. Pat. Nos. 3,126,760, issued to Pierce on Mar. 31, 1964.
Another variable in the design of prior art damping devices has been the use of compression of the rubber component by the inertia ring. In these prior art devices, however, the compression has not been uniform, resulting in non-uniform strain. For example, in U.S. Pat. No. 4,378,865, issued to McLean on Apr. 5, 1983, there is disclosed a torsional damper in which the rubber component is sandwiched between two discs forming the inertia ring. The rubber component and the inertia discs are described as having "complementary" tapered surfaces, i.e. having the same angle. The rubber component increases in thickness with radial extent. Consequently, compression of the rubber component by the complementary angled surfaces of the inertia discs causes the rubber component to be compressed by the same distance. However, because the rubber varies in thickness, the percentage of compression decreases with radial extent, and there in non-uniform compression of the rubber in the McLean device.
Other examples of a device having complementary angled surfaces for the rubber component and the inertia ring are the devices of U.S. Pat. Nos. 3,196,710 and 2,049,133, issued to Pierce on July 27, 1965 and July 28, 1936, respectively. Similar devices are also shown in U.S. Pat. Nos. 2,585,382, issued to Guernsey on Feb. 12, 1952 and 2,861,472, issued to Hansz on Nov. 25, 1958.